Top unloading silo unloaders are used in tower silos to remove material stored in the silo. These unloaders have collectors that are driven around the silo walls to gather material and move it to impeller assemblies which eject the material from the silos. Drive structures, such as surface engaging wheels and hubs, and ring and gear drives, are used to continuously move the collectors around the silo walls. Examples of silo unloader collector drives are shown in the following U.S. patents. Buschbom in U.S. Pat. No. 3,139,995 discloses a drive hub operable to move a top unloading silo unloader around a tower silo. The hub located laterally of the auger collectors and impeller is adjustable to provide a selected amount of pressure on the silo unloader wall engaging wheels. Kucera in U.S. Pat. No. 3,229,828 shows a silo unloader having a power transmission that produces a torque when operated which causes the collector to move around the silo. The power transmission has a drive gear off-set from the upright axis of rotation of the unloader engageable with a driven gear so as to rotate the collector chain and move the collector around the silo. Buschbom et al in U.S. Pat. No. 4,170,385 discloses a silo unloader having driven wheels adjacent opposite sides of the collector. The wheels being driven on the surface of the material disturb the material and reduce the efficiency of the collector.
Top unloading silo unloaders are used with different types of materials that are stored in the silo, such as silage, haylage and the like. These materials have varying degrees of compactness within the silo. Some of the material is loose while others is extremely hard, such as frozen silage. The auger collectors of the silo unloaders, when operating with frozen or very compact material, tend to bounce thereby reduce smooth and efficient operation of the silo unloader.